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The AAPG/Datapages Combined Publications Database

Indonesian Petroleum Association

Abstract


14th Annual Convention Proceedings (Volume 1), 1985
Pages 83-103

Hydrocarbon Prospects in Complex Paleo Subduction Zones

John A. Katili, Soekendar Asikin

Abstract

The possible occurrence of hydrocarbon deposits in complex paleo subduction zones has recently been advanced in various literature.

In this connection it is of interest to compare the outer-arc ridge of western and eastern Indonesia in order to evaluate the hydrocarbon potentials in the chaotic wedges in both areas.

The arc-trench system in western Indonesia was formed by subduction of the Indian Ocean oceanic crust beneath the Eurasian continental crust. No significant hydrocarbon occurrence was reported in the accretionary wedge of western Indonesia. The fore-arc basin, west of Sumatra, typically lacks the coarse quartz rich sediments necessary for clastic reservoir formation. The heatflow and hydrocarbon source rocks are immature.

The arc-trench system of eastern Indonesia shows an entirely different character. Two distinct phases can be discerned in the development of the Banda Arc. In an earlier phase, oceanic crust of the Indian-Australian plate was subducted under the Banda oceanic plate, and in a later phase followed by subduction of the Australian continental crust into the Banda Arc subduction zone.

Whereas the oceanic crust dipping in the Sumatra-Java Trench is only covered by relatively thin pelagic sediments, large parts of the shelf and slope sequences of the Arafura Platform are carried passively on top of the Australian lithospheric plate down into the Tanimbar Trench and Aru Through. The more consolidated lower part of the sequence has a greater shear strength and consequently little material from these sequences was scraped off and incorporated in the chaotic wedge. If these older sediments are rich in organic material, the tectonic processes in the trench and beneath the chaotic wedge in combination with increasing burial depth will enhance the maturity of the organic material. If reservoir rocks exist in front of the chaotic wedge, upslope migration and accumulation must be considered as possible within the faulted blocks in these rocks.

Due to the similarity in geological, tectonic and stratigraphic conditions, the oil and gas occurrence in the subduction complex of eastern Sulawesi might be explained in the same way, although the basic problem which has to be solved first is the past geotectonic position of Sulawesi vis a vis the Australian continental crust of the Vogelkop area in Irian Jaya.


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